1. Field of the Invention
The invention lies in the field of packaging technology and relates to a method and to a device for packaging flat objects, according to the preamble of the respective independent patent claims. The device according to the invention serves for packaging flat objects, for example printed products or of stack-like groups of printed products. Individual printed products or stacks of printed products and other flat objects, such as CDs, sample objects or sample sachets, may be packaged.
2. Description of Related Art
It is known to package flat objects of the type mentioned above with the help of a quasi-endless packaging material web, e.g. plastic film fed from a roll, film from natural materials (eco-film) or paper. Thereby, such a packaging material web is applied around the objects which are conveyed one after the other in a row and distanced from one another, or a packaging material web is fed to such a row on both sides. Then, the packaging material web is closed in the longitudinal direction on the upper side of the row or laterally thereof, in longitudinal seams, and between in each case two consecutive objects transversely to the longitudinal direction, in transverse seams. As the case may be, the objects which are enclosed by the packaging material on all sides in this manner are also separated from one another directly after creating the transverse seams or simultaneously with this.
With the use of plastic film as a packaging material, the longitudinal seams and transverse seams are usually created by way of welding, wherein the separation of the packaged objects may be carried out simultaneously with the creation of the transverse seams.
For processing operations such as welding, gluing etc., the objects are conveyed into a processing device and conveyed out of this again. The processing device is advantageously designed in a manner such that the conveying of the objects to be packaged does not need to be interrupted for the processing, but may be operated in a continuous manner. The objects therefore normally lie on a conveyor rest of a conveyor unit and on this, are moved into or through the processing region of the processing device.
Corresponding processing devices are known from WO 2005/118402, WO 2007/147269 or WO 2009/039673. With the welding devices described there, the welding tools have downholders which are arranged laterally of the processing-active zone (of the hot welding bar). These serve for pressing the packaging material web against the conveyor surface, in the region between two adjacent objects which are, however, distanced from one another, and in the direct vicinity of the welding seam to be created. The downholders are set up such that the two regions of the material web to be connected are firstly pressed against one another on both sides of the envisaged welding seam, and against the conveyor surface. Only then is the hot processing-active zone lowered onto the material. The packaging material is held in a smooth manner directly before this welding process and the quality of the connection is improved by way of these packaging material web downholders.
However, the following problem occurs with the known packaging material web downholders: The processing tool, for processing, exerts a certain force onto the packaging material web and thus indirectly onto the conveyor rest. The conveyor rest as a rule is yielding. For example, it is the case of a conveyor belt of a belt conveyor, which may yield under loading. The conveyor belt may also comprise a compressible layer. The compliance of the conveyor rest, above all with heavier objects, e.g. stacks of different printed products, leads to the objects being able to be displaced in the packaging material web, when the pressure due to the processing tool is relieved and the conveyor rest springs back. The fresh, still soft welding seam is loaded and possibly compromised by way of this. Thereby, it may come to pass that individual packaging units, thus individual objects packaged into bags of packaging material, are dislocated on the conveyor surface. This is disadvantageous, above all for the further processing steps, such as e.g. the gripping of the individual packaging units.
It is therefore the object of the invention to specify a device and a method, with which the mentioned problems are avoided. In particular, a good control of the position of the objects is to be ensured at all times before, during and after the processing.